Recherche avancée

Sur d’autres sites (5955)

• Trying to crop an image in ffmpeg using alphamerge but produces wrong alpha

  12 septembre 2021, par Alex Styl

  I am using alphamerge in order to crop an image within a circle.

  


  What I have so far is :

  


  ffmpeg -f lavfi -i "color=c=white:size=240x240" -i avatar.png -i mask.png -filter_complex \
 "[1][2]alphamerge[img]; \
 [0][img]overlay[out]" -c:v png -map "[out]" -pix_fmt rgba -t 5 -y out.mp4 2>&1


  


  with avatar.png and mask.png respectively being :

  


  

  


  This produces the following output (1 frame of the output video) :

  


  

  


  which is unexpected, given the original input is much darker than this.

  


  How can I crop the 'avatar.png' using the 'mask.png' so that the output is the avatar.png cropped in a circle and keeping the same alpha ?

  


  PS : The important bit here is for me to be able to crop the original image and maintaining the correct colors/apha of the original image. If there is an other way of doing this (other than alphamerge) I am happy to hear it.

  


• can ffmpeg detect monochromatic parts of a video and conditionally set filter parameters accordingly

  15 juillet 2021, par Silentfury

  I have input videos that switch back and forth between coloured and monochrome/grey parts (frames that only contain luma information). Is there a way in ffmpeg to detect whether the current frame is coloured or monochrome and is it possible to use this information to change the parameters of a filter ?

  


  As an example I want to apply the mpdecimate filter and I want it to use a "hi" parameter of 50 (per pixel) for coloured frames and 20 for monochrome frames.

  


  So in pseudo code I want something something like

  


  -vf mpdecimate=hi=if(coloured,64*50,64*20)

  


  but obviously the "coloured" condition doesnt work that way.

  


  Is that somehow achievable ?

  


  PS :
Concernig the detection of monochrome frames I have identified two filters that have a related functionality but I am unable to use the information in another filter :

  


  

  • "geq" can get a good idea of frame colors using cbsum(x,y) and/or crsum(x,y)

  


  • "signalstats" can use the property "SATMAX" to tell about the color level of a frame

  


  


  Is there any way to use the resulting number of any of the two above filters in another filter ?

  


• ffmpeg-concat created almost 80GB of raw files to merge 3 videos with 500ms crossfade of total size about 42MB. how to reduce storage requirement ?

  2 février 2023, par Mayank Kumar Chaudhari

  Yes, I was quite shocked when I found out that my videos were not concatenated due to lack of storage. Then I tried to debug and on the bash terminal I found location of temp files that ffmpeg-concat created.

  


  Good thing is that it deletes these files automatically once the conversion is done but the amount of disk space it used is shocking. It took almost 70-80GB of storage for creating video of about 42MB and probably this is the reason why it takes about 15-20min to create video of about 3-6min.

  


  I tried a lot of other ways like ffmpeg -safe 0 -f concat -i mylist.txt -c copy o.mp4, but it created very bad video — all I could see on video is random colors.

  


  Can anyone suggest a better alternative to concat 3 videos, if possible with crossfade transition.